The present invention relates generally to inkjet printing systems utilizing reciprocating inkjet printhead carriages and encoders for detecting the lateral position of the inkjet printer carriage and, more particularly, to a method for synchronizing print start position for an inkjet printhead carriage utilizing a low-pass filter on the encoder signal.
Thermal inkjet printer mechanisms that utilize printhead having heater resistors for ejecting small ink droplets from the printhead are well-known. The ejection of a multitude of the small ink droplets at controlled locations on a printing substrate produces a desired printed image. In one such printer mechanism, the printhead is typically housed within a carriage that reciprocates back and forth laterally across the substrate, where the printhead includes a plurality of nozzles for ejecting the droplets onto controlled locations of the substrate. An optical encoder (or other type of sensor) is also housed within the carriage and the encoder traverses back and forth along an encoder strip to provide information to the printer controller relating to the lateral position of the carriage with respect to the substrate.
Many inkjet printers print with a maximum resolution that is significantly greater than the resolution of the optical encoder. For example, it is well known to have an inkjet printer with a maximum resolution of 1200xc3x971200 dpi, where the feedback for the horizontal dimension in most cases is an optical encoder with a resolution of 150 lines per inch (1 pi). Therefore, in order to achieve a resolution of 1200 dpi, the encoder signal is divided into as many as eight parts or slices. These slices are generated so that they can provide even distribution of the allotted time period (i.e., the time between encoder pulses, or time to travel {fraction (1/150)}th of an inch), based upon the last measured time period. The slices are used to generate pseudo-fire pulses in logic hardware, which are in turn used to generate fire pulses that activate the printhead mechanisms or nozzles. When the encoder signal is changing quickly, or is corrupted with high frequency noise, print quality may be adversely affected.
In the present invention, a filter, such as a digital phase-locked loop (DPLL), is used to create the pseudo-fire pulses directly from the encoder signals. The DPLL will generate a digital signal whose frequency is a multiple of the encoder signal frequency and is in phase with the encoder signal. This signal produced by the DPLL will be used as the pseudo-fire pulse signal from which fire pulses to the printhead are generated. The DPLL provides a low-pass filtering of the encoder signal, which results in better dot placement capability.
A frequency multiplying property of the DPLL can be easily varied to allow the frequency of the output signal to be a selectable multiple of the output signal. This characteristic provides for a varying addressable print resolution, which can be used for either future higher resolution products, or better alignment features on a 1200 dpi inkjet printer. In the above example, by changing the divider component of the DPLL to 16, the addressable printer resolution will become 2400 dpi.
Because of the filtering properties of the DPLL, the rising edges of the unfiltered encoder signal may not precisely coincide with the corresponding rising edge of the filtered pseudo-fire pulse signal. The signals may exhibit some misalignment depending upon the filter characteristics. Accordingly, the present invention provides methods for synchronizing the print start positions of the inkjet printhead utilizing such a DPLL.
Accordingly, it is a first aspect of the present invention to provide a method for synchronizing the print start position for a printer carriage on an inkjet printer that includes the steps of: (a) providing an encoder signal indicative of a position on an inkjet printer carriage relative to either the substrate being printed upon or a printer platen; (b) filtering the encoder signal to provide a filtered encoder signal; (c) detecting an activation in the encoder signal preceding a predetermined print start position of the printer carriage; (d) upon detection of the activation of the encoder signal in step (c), detecting a next deactivation of the filtered encoder signal; (e) upon detecting the next deactivation of the filter encoder signal in step (d), detecting a count of the next activations of the filtered encoder signal; and (f) assigning a synchronized print start position at an end of a count. In a more detailed embodiment, the count is one or more of the next activations of the filtered encoder signal. In yet a further detailed embodiment, the method further comprises the step of calculating the count based, at least in part, upon a difference between a carriage position corresponding to the activation of the encoder signal detected in step (c) and the predetermined print start position.
In an alternate detailed embodiment of this first aspect of the present invention, the encoder signal and the filtered encoder signal are alternating voltage level signals, alternating at an encoder signal frequency and a filtered encoder signal frequency, respectively; the activation of the encoder signal is the rising edge of the encoder signal; the activation of the filtered encoder signal is the rising edge of the filtered encoder signal; and the deactivation of the filtered encoder signal is the falling edge of the filtered encoder signal. In a further detailed embodiment, the step of filtering includes a step of multiplying the encoder signal frequency to produce a filtered encoder signal frequency that is a multiple of the encoder signal frequency. In yet a further detailed embodiment, the multiple of the encoder signal frequency for the filtered encoder signal frequency is selectable. In yet a further detailed embodiment, the filter is a digital phase-locked loop (DPLL).
It is a second aspect of the present invention to provide a method for synchronizing the print start position for a printer carriage on an inkjet printer that includes the steps of: (a) providing an encoder signal indicative of a position of an inkjet printer carriage relative to a substrate being printed upon or a printer platen, where the encoder signal is an alternating voltage signal with an encoder signal frequency; (b) filtering and dividing the encoder signal to provide a fire pulse signal, where the fire pulse signal is an alternating voltage signal with a fire pulse signal frequency that is a multiple of the encoder signal frequency; (c) detecting a rising edge of the encoder signal preceding a predetermined print start position of the printer carriage; (d) upon detection of the rising edge of the encoder signal in step (c), detecting a next falling edge of the fire pulse signal; (e) upon detection of the next falling edge of the fire pulse signal in step (d), detecting a count of the next rising edges of the fire pulse signal; and (f) assigning a synchronized print start position at an end of the count. In a further detailed embodiment, the method further includes a step of calculating the count based, at least in part, upon a difference between a carriage position corresponding to the rising edge of the encoder signal detected in steps (c) and the predetermined print start position.
A third aspect of the present invention is directed to a method for synchronizing the print start position for a printer carriage on an inkjet printer that includes the steps of: (a) providing an encoder signal indicative of a position on an inkjet printer carriage relative to either a substrate being printed upon or a printer platen; (b) filtering the encoder signal by a first filter to provide an intermediate encoder signal; (c) filtering the intermediate encoder signal by a second filter to provide a filtered encoder signal; (d) detecting an activation in the encoder signal preceding a predetermined print start position of the printer carriage; (e) upon detection of the activation of the encoder signal in step (d), detecting a next deactivation of the intermediate encoder signal; (f) upon detecting the next deactivation of the intermediate encoder signal in step (e) detecting a first count of the next activations of the intermediate encoder signal; (g) at an end of the first count, detecting a next deactivation of the filter encoder signal; (h) upon detecting the next deactivation of the filtered encoder signal in step (g) detecting a second count of the next activations of the filtered encoder signal; and (i) assignment a synchronized print start position at an end of the second count. In a more detailed embodiment, the method further includes the steps of: calculating the first count based, at least in part, upon a difference between a carriage position corresponding to the activation of the encoder signal in step (d) in the predetermined print start position, and calculating the second count base, at least in part, upon the difference between the carriage position corresponding to the end of the first count and the predetermined start position.
In an alternate detailed embodiment of the third aspect of the present invention described above, the encoder signal, the intermediate encoder signal and the filtered encoder signal are alternating voltage level signals, alternating at an encoder signal frequency, an intermediate encoder frequency and a filtered encoder signal frequency, respectively; the activation of the encoder signal is the rising edge of the encoder signal; the activation of the intermediate encoder signal is the rising edge of the intermediate encoder signal and the deactivation of the intermediate encoder signal is the falling edge of the intermediate encoder signal; and the activation of the filtered encoder signal is the rising edge of the filtered encoder signal and the deactivation of the filtered encoder signal is the falling edge of the filtered encoder signal. In yet a further detailed embodiment, the step (b) of filtering the encoder signal includes a step of multiplying the encoder signal frequency to produce and intermediate encoder signal frequency that is a multiple of the encoder signal frequency, and the step (c) of filtering the intermediate encoder signal includes a step of multiplying the intermediate encoder signal frequency to produced a filtered encoder signal frequency that is a multiple of the intermediate encoder signal frequency.
A fourth aspect of the present invention is directed to a method for synchronizing the print start position for a printer carriage on an inkjet printer that includes the steps of: (a) providing an encoder signal indicative of a position of an inkjet printer carriage relative to either a substrate being printed upon or a printer platen, where the encoder signal is an alternating voltage signal with an encoder signal frequency; (b) filtering and dividing the encoder signal to provide an intermediate encoder signal, where the intermediate encoder signal is an alternating voltage signal with an intermediate encoder signal frequency that is a multiple of the encoder signal frequency; (c) filtering and dividing the intermediate signal to provide a fire pulse signal, where the fire pulse signal is an alternating voltage signal with a fire pulse signal frequency that is a multiple of the intermediate signal frequency; (d) detecting a rising edge of the encoder signal preceding a predetermined print start position of the printer carriage; (e) upon detecting of the rising edge of the encoder signal in step (d), detecting a next falling edge of the intermediate encoder signal; (f) upon detection of the next falling edge of the intermediate encoder signal in step (e), detecting a first count of the next rising edges of the intermediate encoder signal; (g) at an end of the first count, detecting a next falling edge of the fire pulse signal; (h) upon detection of the next falling edge of the fire pulse signal in step (g), detecting a second count of the next rising edges of the fire pulse signal, and (i) assigning a synchronized print start position at an end of the second count. In a further detailed embodiment, the method further includes the steps of calculating the first count base, at least in part, upon a difference between a carriage position corresponding to the rising edge of the encoder signal in step (d) and the predetermined start position, and calculating the second count based, at least in part, upon a difference between the carriage position corresponding to the end of the first count and the predetermined print start position.